In all secondary and tertiary enhanced oil recovery processes, in which a drive fluid is used to force oil from an injection well to a production well, profile control may be needed to overcome the deleterious effects of formation permeability stratification. When formation permeability inhomogeneity is encountered, injected and driven fluids preferentially travel through the most permeable regions, resulting in low sweep efficiency and bypassing of oil in lower permeability regions. Another problem is that certain injected fluids may be much lighter than the reservoir fluids and so will separate by gravity, rising toward the top of the flowing region and resulting in bypassing of lower regions (gravity override). One commonly employed solution to these problems is to inject a material that will preferentially flow into the more permeable regions (or is selectively introduced into higher regions) but will subsequently impede further flow through them, thus diverting flowing fluids into previously uninvaded regions. Polymer gels, or polymer/gelling agent mixtures that will subsequently gel in situ, can be used.
The enhanced oil recovery techniques of waterflooding, CO.sub.2 flooding, miscible or immiscible gas flooding, and steam flooding are of particular interest and importance. Profile control can often improve performance in such processes by reducing the effects of permeability stratification or gravity override. A gel suitable for profile control must be stable enough to continue to impede flow for long periods of time at the reservoir temperature, salinity and pH. There are a variety of materials commercially available for profile control, all of which perform differently and have limitations. Biopolymers such as xanthan gums are unstable above about 140.degree. F. Synthetic polyacrylamides, depending upon their degree of hydrolysis and the nature and amount of other functional groups such as alkyl sulfonate or pyrrolidone, will have a temperature above which they will not be useful at a given salinity.
Therefore, what is needed is an economical gel which can be used for profile control during enhanced oil recovery under the harsh conditions encountered in a subterranean formation.